1. Field
The present invention relates generally to the conversion of starches to sweeteners and more particularly to the preparation of high fructose sweeteners from impure barley flour.
2. State of the Art
Starch syrups have been prepared in the past by the hydrolysis of starch suspensions and cereal slurries. Hydrolysis has been effected by heating these solutions and slurries in the presence of dilute acids and by enzyme action. Representative acid amylolysis processes ae shown in U.S. Pat. Nos. 3,200,012 (Hay); 432,358 (Berge); 690,359 (Brown); 2,438,033 (Brown et al); 2,797,176 (Gottfried et al); 2,073,342 (Hart); 246,262 (Williams et al); 2,094,558 (Daly); 1,938,574 (Bauer); 3,383,245 (Scallet et al). In general, these processes involve the breakdown of starch granules, which contain two polymers of (amylose and amylopectin) into glucose units; and the concentration of the glucose into syrups.
Processes utilizing both acid hydrolysis and enzymatic action are described in U.S. Pat. No. 2,137,973 (Daly et al). The combined acid and acid enzyme processes of the prior art described by Daly et al have certain drawbacks, among them being a characteristic bitter taste in the acid-converted syrup when it is concentrated to in excess of about 60 D.E. Various methods are known for minimizing this bitterness. The use of ion exclusion and/or ion exchange columns to eliminate acid by-products is disclosed by U.S. Pat. No. 3,305,395 (Scallett et al) to produce a non-crystallized, very sweet tasting syrup of about 70 to 85 D.E. Crystallization techniques to extract the glucose crystals free from acid by-products in the liquor are discribed in U.S. Pat. Nos. 3,265,533 (Meisel); and 3,236,687 (Smith et al).
An ancient patent disclosing a crude enzymatic process is U.S. Pat. No. 260,853 (Duff). The source of enzymes in that process was "malt". More modern enzyme conversion methods avoid the use of mineral acids in favor of a three enzyme process to convert starch solutions into high fructose sweeteners. These enzymatic catalysis reactions have the advantage of being quite specific so that they avoid the side reactions inherent in the aforedescribed highly acidic hydrolysis methods of producing sweeteners. In the typical sequence of these processes, the starch is first treated with alpha-amylase (alpha-1, 4-Glucan gluconohydrolase) to break down the starch into smaller water soluble fragments in a liquefaction process such as that described by U.S. Pat. No. 3,185,633 (Krebs). These starch fragments are then reacted with glucoamylase (alpha-amyloglucosidase alpha-1, 4-Glucon glucohydrolase) to degrade the fragments into individual glucose molecules. The glucose solution is then treated with glucose isomerase (glucosephosphate isomerase; D-Glucose-6 phosphate ketol isomerase) to convert a portion of the glucose into fructose, and the fructose solution is subsequently purified and concentrated into a colorless syrup. See, for example, U.S. Pat. Nos. 3,285,770 and 3,383,245 (Scallet). Other examples of three enzyme processes for preparing starch syrups from starch solutions are found in U.S. Pat. Nos. 2,891,869 (Langlois); 3,137,639 (Hurst); 3,305,395 (Scallett); and 3,067,066 (Ehrenthal). The historical development and the nature of these three enzyme conversion methods are described by R. V. MacAllister, E. K. Wardrip, and B. J. Schnyder in their article "Modified Starches, Corn Syrups Containing Glucose and Maltose, Corn Syrups Containing Glucose and Fructose, and Crystalline Dextrose", contained in the series of monographs entitled Enzymes In Food Processing (Academic Press Inc.; New York, 1975), edited by Gerald Reed. The entire series is descriptive of the technology pertinent to this invention, and is incorporated by reference as a portion of this disclosure.
None of the present three enzyme processes produce a purified and highly concentrated syrup (that is, in excess of about 95 D.E.) directly from the enzyme treatment of slurries of impure starch flour. Most of the present methods for producing such syrup, for example, include a starch recovery step to isolate purified starch prior to enzyme treatment. The use of corn grits as a starting raw material without prior starch separation has been suggested for the preparation of a sweetener. This approach has not yet succeeded commercially because of the inferior quality of the final product, even though the impurities associated with the corn grits are relatively benign when present during the starch hydrolysis procedure. Although the technology for converting purified starch to sweetener is well developed, it has not been successfully applied to the converting of starch sources rich in glucan gums such as are found in barley grains. The presence of these gums interferes with conventional liquification, saccharification and purification procedures. Under the conditions of the aforementioned prior art processes for the production of sweetener from starch, these gums generate high viscosities at low concentrations. This limitation leads to: excessive dilution and high evaporation costs; difficulties in achieving a liquid/solids separation for the removal of insoluble and colloidal impurities; and a low quality final product which is high in color and turbidity, is impure and tends to gelatinize at a concentration of about 70% solids. For the same reasons, it has not been possible to achieve an economical separation of barley starch from barley flour. Accordingly, it has not been practical to produce a purified and concentrated sweetener using barley as the raw material source.